New electronic devices are constantly becoming more powerful and more compact. High power components, including RF/microwave electronics, diode lasers, light emitting diodes (LED), insulated gate bipolar transistors (IGBT), central processing units (CPU), etc., are utilized in a wide variety of industries such as telecommunications, automotive, aerospace, avionics, medical, and materials processing. With these smaller more powerful devices comes an increased requirement to dissipate the heat generated by the devices. The electronics can be damaged by temperature buildup if heat generated during operation is not sufficiently or effectively dissipated. New capabilities and designs are constrained by the ability of designers to remove heat in a cost-effective manner.
LED's are rapidly replacing other lighting solutions in everyday applications. This trend is also seen in the automotive sector. Interior lights have been largely replaced by more efficient, longer lasting LED's, as are some of the exterior lights such as brake lights and turn indicators. With the increase in white LED output power and efficiency, LED headlights are now no longer reserved for high-end luxury vehicles. It is estimated that by 2020, twenty percent of all cars will be equipped with LED headlights. A very similar trend has been observed on video projectors for consumer and commercial uses. Changing from incandescent or high intensity discharge (HID) lighting to LED presents a new set of design challenges. Even though LED is very efficient in converting electricity into light, 70% to 80% of the energy input is dissipated as heat.
Conventional thermal management products for LEDs are typically constructed of either copper (Cu) or aluminum (Al). Such thermal management products are commonly used for extracting heat from a heat source and dissipating the heat into surroundings. Generally, copper is utilized for thermal management at chip levels and aluminum is utilized for higher level thermal management, such as a heat spreader. With the thermal conductivity of copper and aluminum of around 120 to 400 W/m-K, aluminum and/or copper thermal management systems are limited in terms of maximum power loading and design options.
For conventional heat spreaders or heat sinks for LED systems, attempts to provide good thermal management have included increasing cross-section of heat paths, enlarging heat dissipation area, and/or installing forced air cooling or liquid cooling, among other options. However, such attempts require increased dimensions, weight, structure complexity, cost, and/or limit design possibilities. Further, forced air cooling and/or liquid cooling systems are subject to their own limitations or unreliability.
Thermal pyrolytic graphite (TPG), with its metal encapsulated composites (e.g., TC1050® available from Momentive Performance Materials), is an advanced thermal management material serving military and aerospace industries for over a decade. Thermal pyrolytic graphite is formed via a two-step process that provides well-aligned graphene planes to provide a material with superior thermal conductivity (e.g., greater than 1500 W/m-K). Compared to copper, which is commonly used in passive cooling and the most thermally conductive among all the materials mentioned above, thermal pyrolytic graphite can provide four times the cooling power at ¼th the weight of copper.
Traditionally, heat spreaders comprising thermal pyrolytic graphite are formed by encapsulating thermal pyrolytic graphite into a metal casing, such as aluminum, copper, etc. via a diffusion bonding process. Such a process is described in U.S. Pat. No. 6,661,317. The encapsulated thermal pyrolytic graphite composite parts behave like solid metal and can be further machined, plated, or bonded to other components to meet various customers' requirements.